Various types of valves are used in the semiconductor industry to control the flow of fluids, including highly caustic fluids. It is essential that these valves do not cause quiescent or dead spots in the fluid flow course which could cause the fluid to become stagnant and degrade or could trap solids resulting in the contamination of the fluid. Fluid flow rates in semiconductor fabrication sometimes must be of a significant quantity, and it is important that any valves used in a piping system do not cause undue pressure loss or restriction in flow rate. In addition, it is important that the number of potential leakage sources or seals be kept to a minimum due to the highly caustic fluids often used in the semiconductor industry.
These valves must be made of materials highly resistant to the caustic fluids. Contact of the caustic fluids with metal parts is generally to be avoided. The components which contact the fluids are typically formed of fluoropolymers such as perfluoroalkoxy (PFA), polyvinylidene (PVDF), or polytetrafluoroethylene (PTFE). Typically, the portions of the valve in direct contact with the fluid, such as the valve body, valve and valve seat, the primary diaphragm, and seals or gaskets will be formed from fluoropolymer material.
Flow restriction through a poppet valve may be lessened by increasing the gap between the valve and valve seat, usually by lifting the valve a greater distance with an extended stroke actuator. In valves using fluoropolymer diaphragms, however, a problem is that such diaphragms do not generally have a long fatigue life, tending to wear out in a relatively short time. Moreover, fluoropolymer diaphragms having sufficient flexibility to function properly with an extended stroke actuator can be delicate and may be easily overstressed, leading to premature failure of the valve. Valve failure in critical semiconductor processing operations may result in expensive delays in processing and damage to critical equipment and product.
What is still needed in the industry is an extended stroke poppet valve for caustic fluids having features enabling an extended service life for the valve.